Method of manufacturing a hydrosensitive element for a humidity sensitive device

ABSTRACT

A hygrosensitive element is produced by passing a flexible, smooth, dielectric film uniformly and continuously in succession through a solution of gelatin and then through an aqueous solution of a hygroscopic salt and a tanning agent for the gelatin. A layer of gelatin of uniform thickness is formed on the film and the salt is uniformly distributed throughout the gelatin layer. The layer is dried, exposed to light to tan or harden the gelatin and then the strip is cut into separate film elements.

United States Patent [1 1 Gabrusenok 51 Oct. 29, 1974 METHOD OF MANUFACTURING A HYDROSENSITIVE ELEMENT FOR A HUMIDITY SENSITIVE DEVICE lnventor: Pavel Stepanovich Gabrusenok,

Sadovaya ul. 24, kv. l2, Leningrad, U.S.S.R.

Filed: May 14, 1973 Appl. N0.: 360,167

Related Application Data Continuation-impart of Ser. No. 160,699, July 8, 1971, abandoned, which is a division of Ser. No. 776,969, Nov. 19, 1968, Pat. No. 3,712,860.

US. Cl 117/219, 117/115, 117/164, 117/933, 73/335, 73/338, 236/44 E, 324/65 R Int. Cl B4411 1/18 Field of Search 117/215, 217, 219, 164, 117/115, 201, 113, 933; 324/65 R; 73/335, 338', 236/44 E References Cited UNITED STATES PATENTS 6/1945 Kersten 324/65 R 2,876,321 3/1959 Amdur 236/44 E 2,937,524 5/1960 Gregor 3,175,400 3/1965 Amdur 236/44 E Primary Examiner-Ralph S. Kendall Assistant Examiner-Michael F. Esposito Attorney, Agent, or Firm-Waters, Roditi, Schwartz & Nissen 9 Claims, 2 Drawing Figures METHOD OF MANUFACTURING A IIYDROSENSITIVE ELEMENT FOR A HUMIDITY SENSITIVE DEVICE CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 160,699, filed July 8, I971, now abandoned, which in turn is a divisional of application, Ser. No. 776,969, filed Nov. 19, I968, now US. Pat. No. 3,712,860.

DETAILED DESCRIPTION The present invention relates to a method for manu facturing a hygrosensitive element for electrolytic humidity responsive devices used in combination with appropriate electrical circuitry in systems for remote measurement, recording and automatic control of humidity in air-conditioning systems and other installations.

Such humidity sensitive devices will be referred to as air'humidity detectors" and it is to be understood that they are applicable to the measurement of the humidity of other gases too, provided they do not attack the materials of the detector.

The electrolytic air humidity detectors known in the art comprise a base or backing or support with electrodes rigidly fastened thereto and a hygrosensitive coating applied to the base over the electrodes, said coating containing a hygroscopic salt and a filmforming binding agent. In such a case the hygrosensitive element is an integral part of the detector. This, as will be explained below, is the main cause of insuff|- cient stability and interchangeability of the currently used electrolytic air-humidity detectors.

One of the main objects involved in increasing the stability and interchangeability of the electrolytic detectors amounts to making a hygrosensitive coating of uniform thickness and concentration and retaining this uniformity in the course of operation. This object cannot be achieved unless the process of application of the hygrosensitive coating is continuous for each batch of detectors because the beginning and end of each process are inevitably marked by some transitional steps exerting a different effect in each particular case on the thickness of the coating applied.

Besides, the hygrosensitive coating must be applied to a homogeneously smooth surface which is free from cracks, sharp changes of shape, joints between different materials, otherwise the capillary forces and adhesion gradient on the base surface may lead to local thickening of the applied coating and to displacement of the hygrosensitive substance during detector operation owing to inconstancy in time of the capillary and adhesion forces.

Of the known methods of application of the hygrosensitive coating the most commonly used are methods in which each detector is dipped into a filmforming hygroscopic solution and uniformly withdrawn therefrom, or the solution is applied to the surface of the detector with a brush.

The above methods fail to ensure high-quality hygrosensitive coatings of the air-humidity dectectors.

Intermittent application of the coating, irregular surface, and heterogeneous materials on the surface of detectors (electric insulating base and metal electrodes) preclude the production of a hygrosensitive coating of uniform thickness and fail to ensure the constancy of thickness in the course of detector operation which necessitates individual calibration and setting of each detector during manufacture and leads to insufficient stability of calibration characteristics in time.

It is, therefore, an object of the present invention to provide a method for producing a hygrosensitive ele ment featureing high stability and interchangeability.

Another object of the present invention is to provide a method of batch production of said hygrosensitive elements.

Still another object of the invention resides in providing an electrolytic detector capable of using the above described hygrosensitive elements.

With these and other objects in view, the present invention aims at providing a method for producing a hygrosensitive element with a homogeneous smooth surface of the base and a hygrosensitive coating of uniform thickness, said element being a separate detachable part of the detector, said method ensuring continuity of application of the hygroscopic coating to the element base.

This objective is achieved by providing a method in which a hygrosensitive element has its coating uniformly applied to a homogeneous, flexible dielectric film.

The flexibility of the backing makes it possible to apply uninterruptedly the hygrosensitive coating to a continuously moving strip, while the homogeneity of said strip ensures stability of the coating thickness along the strip length.

It is practicable to provide for rigid connection of and electric contact with the hygrosensitive element by the use electrodes placed on the hygrosensitive element.

A method of manufacturing hygrosensitive elements according to the invention consists in pulling a flexible strip, e.g., a dielectric film, continuously and at a uniform speed through a solution of gelatin to form a gelatin layer of uniform thickness on said film which layer is then impregnated with an aqueous solution of hygroscopic salt and an added tanning component so that the salt is spread uniformly throughout the layer of gelatin. Then the obtained coating is dried, exposed to light for tanning of the gelatin and cut into separate film elements.

A broad range of well known hygroscopic substances can be used as the hygroscopic salt. In particular, suitable substances are lithium chloride LiCl, zinc chloride ZnCl calcium chloride CaClmagnesium chloride MgCl and a mixture of potassium-sodium tartrate with sodium chloride KNaC H O 4H O NaCl.

Suitable tanning components that can be used are potassium bichromate, ammonium bichromate, formalin, chromium acetate Cr(CH COO) the diglycidic ester of ethylene glycol CH CHO.CI-l OCH OCI-I .CHOCH and mucochloric (dichloroformylacrylic) acid Cl.C(COH):CCl.COOH.

For applying the hygrosensitive coating it is preferred to pull the film through a 10 percent solution of gelatin at a temperature of 36C. then through the aqueous solution of hygroscopic salt and tanning component. The temperature of the gelatin solution is maintained at 36C. because the solution has the maximum viscosity at this temperature, and, consequently, the temperature dependence of the viscosity is minimum.

Now the invention will be better understood from a description of an embodiment given by way of example of a hygrosensitive element and detector with reference to the accompanying drawings in which:

FIG. 1 shows a hygrosensitive element of the present invention; and

FIG. 2 is a sectional view of an air-humidity detector with the element of FlG. l.

A hygrosensitive element 1 has a film support (FIG. 1) comprising a triacetate, nitrocellulose, or other flexible strip whose surface is covered with a hygrosensitive coating 15 to 20 mincrons thick.

Glued to the ends of the hygrosensitive elements are two electrodes 2 made from anti-corrosion metal foil.

The electrolytic air-humidity detector comprises an electric insulating base 3 (FIG. 2) to which a hygrosensitive element 6 is fastened by contact plates 4 and screws 5. On top, the detector is provided with a protective casing 7 with a fine-meshed metal screen 8.

The hygrosensitive elements are manufactured, according to the invention, as follows:

A triacetate, nitrocellulose, or other support of photographic film (provided with a prime or bonding layer) in the form of a long strip moving around a cylindrical shaft and contacting at one side a 10 percent aqueous solution of gelatin at 36C. is pulled through said solution at a uniform speed of 300 cm/min so that the surface of the backing becomes covered with a layer of gelatin 15 to 20 microns thick, accurate within percent. Then, after the coating is dried, the film is then pulled through an aqueous solution of lithium chloride with a specific gravity of from 1.032 to 1.065 g/cm at 20C. with the addition of 5 to 20 ml of aqueous solution of potassium bichromate saturated at 20C per litre of said first named solution. The strip is pulled at a speed of 1 cm/min, the solution temperature being to 18C. so that the gelatin is impregnated with the solution to three-fourths of its thickness. Then the gelatin coating is dried in the course of 5 minutes at 50 to 80C. being simultaneously exposed for 30 minutes to the light of a conventional 100 W incandescent lamp placed at a distance of 50 cm from the film.

The dried film is cut into strips of equal lengths and width and the ends of these strips are provided with glued-on plates 0.05 to 0.1 mm thick made of gold or silver foil.

By pulling the film in succession through the filmforming and hygroscopic solutions, it is possible to ensure a high uniformity of distribution of lithium chloride over the area of gelatin coating while in the previous one stage coating, the film which is pulled only once through a mixture of the film-forming and hygroscopic solutions prevents the gelatin from being used as a film-forming agent; gelatin in this case loses its gelling ability which affects adversely the uniformity of coating thickness.

ln lieu of the lithium chloride, other suitable hygroscopic substances can be employed, and in similar respects other suitable tanning agents are equally applicable.

Moreover, it is equally possible to employ polyvinylacetate instead of gelatin.

Also, the influence of a light is obligatory for hardening gelatin, however, it does not necessarily represent an independent step of the process. Namely, if all the operations are carried out in the light, this usually is sufficient. Moreover, the term light is intended to cover UV light as well.

The speed of pulling the film through the gelatin solution could be substantially reduced still maintaining the same concentration of gelatin in the solution. In this case the gelatin layer formed on the film will be substantially thinner. When pulling at a speed of 5 cm/min the gelatin layer will be about 1 micron thick. This embodiment of the method results in somewhat reduced stability of the produced hydrosensitive elements, but at the same time substantially improves the quickresponse characteristic thereof (due to reduced inertia).

Inasmuch as the above described hydrosensitive element and detector and the method of their manufacture may vary within the spirit and scope of the appended claims it will be understood that the description above does not restrict the invention to these particular embodiments which have been disclosed.

What is claimed is:

1. A method of manufacturing a hydrosensitive element comprising pulling a flexible strip in the form of a dielectric film continuously at a uniform speed through a solution of gelatin for producing on the film a uniform gelatin layer, impregnating the gelatin layer with an aqueous solution consisting of a hygroscopic salt and a tanning component such that the salt is distributed uniformly in the gelatin layer, drying the coating, exposing the coating to light for tanning the gelatin and cutting the strip into separate film elements.

2. A method according to claim 1 wherein the solution of gelatin is a 10 percent aqueous solution, said solution being kept through at a constant temperature of 36C.

3. A method according to claim 2 wherein said strip is successively pulled through said solution of gelatin and the aqueous solution of hygroscopic salt and tanning component.

4. A method according to claim 2 wherein said strip is pulled through said gelatin solution at a speed to form a gelatin layer 15 to 20 microns thick, said strip coated with gelatin then being pulled through the aqueous solution of hygroscopic salt and tanning component so that the gelatin is impregnated to three-fourths of its thickness.

5. A method according to claim 4 wherein the strip speed through the gelatin solution is 300 cm/min and through the aqueous solution of hygroscopic salt and tanning component is 1 cm/min, the temperature of the latter solution being 10 to 18C.

6. A method according to claim 11 comprising drying said gelatin layer on said film before drawing the film through the solution of hygroscopic salt and tanning component.

7. A method according to claim 1 wherein said hygroscopic salt is lithium chloride, zinc chloride, calcium chloride, magnesium chloride, or a mixture of potassium sodium tartrate with sodium chloride.

8. A method according to claim 1 wherein said tanning component is potassium bichromate, ammonium bichromate, formaline, chromium acetate, the diglycidic ester of ethylene glycol or mucochloric acid.

9. A method according to claim 1 wherein said aqueous solution of hygroscopic salt and tanning agent consists of a solution of lithium chloride with a specific gravity from 1.032 to 1.065 g/cm at 20C. and 5 to 20 ml, per liter of solution, of an aqueous solution of potassium bichromate saturated at 20C.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. ,832 DATED October 29, 1974 INVENTOR(S) Pavel S. Gabr'usenok It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Title: Change "hydrosensitive" to --hygrosensitive- Column 4, line 14, change "hydrosensitive" to -hygrosensitive- Claim 1, line 1, change "hydrosensitive" to hygrosensitive Column 1, line 64, change "dectectors" to -detectors-- Column 3, line 10, change "mincrons" to --microns Claim 2, line 3, cancel "through" Signed and Scaled this Sixth D f December I 977 L] Attest:

RUTH C. MASON LUTRELLE F. PARKER Arresting Officer Acting Commissioner of Patents and Trademark;

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION Q PATENT NO. 1 32 DATED I October 29, 1974 INVENTOR(S) Pavel S. Gabr'usenok 1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: r Q r In the Title: Change "hydrosensitive" to ---hygrosensitive-- Column 4, line 14, change hydrosensitive" to hygrosensitive-Z Claim 1, line 1, change "hydrosensitive" to -hygrosensitive-- Column 1, line 64, change "dectectors" to ---detectors Column 3, line 10, change "mincrons" to -microns Claim 2, line 3, cancel "through" Signal and Scaled this Sixth Day Of December 1977 [SEAL] Attest:

RUTH C. MASON LUTRELLE F. PARKER Attesting Ojficer Acting Commissioner of Patents and Trademarks 

1. A METHOD OF MANUFACTURING A HYDROSENSITIVE ELEMENT COMPRISING PULLING A FLEXIBLE STRIP IN THE FOM OF A DIELECTRIC FILM CONTINUOUSLY AT A UNIFORM SPEED THROUGH A SOLUTION OF GELATION FOR PRODUCING ON THE FILM A UNIFORM GELATIN LAYER, IMPREGANTING THE GELATIN LAYER WITH AN AQUEOUS SOLUTION CONSISTING OF A HYGROSCOPIC SALT AND A TANNING COMPONENT SUCH
 2. A method according to claim 1 wherein the solution of gelatin is a 10 percent aqueous solution, said solution being kept through at a constant temperature of 36*C.
 3. A method according to claim 2 wherein said strip is successively pulled through said solution of gelatin and the aqueous solution of hygroscopic salt and tanning component.
 4. A method according to claim 2 wherein said strip is pulled through said gelatin solution at a speed to form a gelatin layer 15 to 20 microns thick, said strip coated with gelatin then being pulled through the aqueous solution of hygroscopic salt and tanning component so that the gelatin is impregnated to three-fourths of its thickness.
 5. A method according to claim 4 wherein the strip speed through the gelatin solution is 300 cm/min and through the aqueous solution of hygroscopic salt and tanning component is 1 cm/min, the temperature of the latter solution being 10* to 18*C.
 6. A method according to claim 1 comprising drying said gelatin layer on said film before drawing the film through the solution of hygroscopic salt and tanning component.
 7. A method according to claim 1 wherein said hygroscopic salt is lithium chloride, zinc chloride, calcium chloride, magnesium chloride, or a mixture of potassium sodium tartrate with sodium chloride.
 8. A method according to claim 1 wherein said tanning component is potassium bichromate, ammonium bichromate, formaline, chromium acetate, the diglycidic ester of ethylene glycol or mucochloric acid.
 9. A method according to claim 1 wherein said aqueous solution of hygroscopic salt and tanning agent consists of a solution of lithium chloride with a specific gravity from 1.032 to 1.065 g/cm3 at 20*C. and 5 to 20 ml, per liter of solution, of an aqueous solution of potassium bichromate saturated at 20*C. 